How to check if any frontend user is logged in

To determine from TypoScript if a frontend user is logged in and do something based on this and something else if there is no frontend user logged in, then you need to set up some conditions in your page typoscript, something like this:

[usergroup=*]

#here you do something if there is a frontend user logged in

[else]

#here you do something else if there is no frontend user logged in

[global]